Leadplant
(Amorpha canescens) in bloom in a prairie garden. Very few native prairie plants show off quite as much as this subshrub. It is as if it is saying, ‘Hey, look at me! I’m special!.’
MIKE MILLER

Nature enthusiasts usually don’t have a problem differentiating between a tree and an herbaceous plant. Sometimes the differentiation between a tree and a shrub is a bit more of a grey area … “Is it a large shrub, or a small tree?” But still, it is fairly easy to tell a shrub from an herbaceous plant.

MIKE MILLER

Shrubs have growth buds located along a woody stem. They grow from these branch-buds the next year. Herbaceous plants do not have woody stems. Their growing buds are below ground, and when the plants go dormant in the fall, they pop up from those underground roots.

Nature enthusiasts also know that plants don’t necessarily follow our preconceived notions of how they should behave. Enter the realm of the “subshrub.” These types of plants have woody bases that produce growth that resembles herbaceous plants. When the plant goes dormant, it dies back to the woody base. This growth pattern is common in plants adapted to grow in harsh desert conditions. Some common garden plants such as sage, rosemary, and thyme are subshrubs. Sorry Scarborough Fair fans, parsley is an herbaceous plant.

In Illinois, native subshrubs are uncommon, but there are some that can be found on a summer stroll through an Illinois prairie. It makes sense that a few subshrubs would find a suitable habitat in our tallgrass prairie. Frequent prairie fires favor the adaptive advantage of herbaceous plants with buds protected below the soil surface. Subshrubs have enough below ground buds to ensure they can survive a prairie fire, but they can also have growth buds above ground to give them a “limb-up” on competition during years when fire is less frequent.

One of my favorite prairie subshrubs is Leadplant (Amorpha canescens), a member of the Bean family. It gets its name from the “leaden” color and texture of its mature leaves. The leaves are feather-like and covered with fine grayish hairs that make it stand out. Its flowers are quite striking: A spike of royal purplish-blue flowers with prominent reddish stamens tipped with conspicuous yellow anthers. Very few native prairie plants show off quite as much as this subshrub. It is as if it is saying, “Hey, look at me! I’m special!” That is exactly what it is saying to the insect world. There is a long list of native bees that are attracted to the pollen of its conspicuous flowers. The leaves are important food to several insects which, in turn, are food for grassland birds. The plant is an important forage plant for many prairie mammals ranging from ground squirrels to bison.

The roots of Leadplant are no less amazing than their above ground counterparts. Delving into the soil up to 16 feet, the roots have a close association with a specific rhizobium bacterium. Root nodules form creating a habitat for this bacterium to thrive. In trade for this home, the bacterium will produce excess nitrogen which benefits the plant. This allows Leadplant to grow in a wide range of soil conditions. A good place to see Leadplant growing in our area are the glacial drift hill prairies in Robinson Park, Camp Wokanda, and Singing Woods Nature Preserve. It is a true prairie species and is an indicator of high quality, undisturbed natural areas.

Luckily, Leadplant is also easy to add to a prairie garden. Seeds can be purchased or collected in the fall. Like most native plants, they need to go through a cold-moist stratification process to break dormancy. Seeds can be overwintered in an outdoor planting bed for natural stratification. They can also be stratified indoors for greater protection from seed predators. Simply place the seeds in a plastic bag with moist sand. Pop them in the refrigerator for 40 to 60 days and then plant them in a seed starter mix. Transfer sprouts into pots containing some native soil with natural soil microbes. You can also purchase rhizobium innoculant from native plant nurseries to add to your soil. Give the seedlings plenty of direct light and transfer them to their permanent home once they harden off. It might take a couple of years before you see flowers, but it is worth the wait.

Leadplant grows best in full sun but can tolerate some shade. To maintain the plant, feel free to prune back the branches in early spring. Don’t be afraid to prune back to the ground if it gets to “leggy” or sprawls out. It is a prairie subshrub, built to withstand prairie fires and bison grazing, so it can tolerate inept gardeners as well.